I do this all the time, when my wife asks me a Y/N question and then turns it into multiple choice just as I'm about to answer: "Do you want to go out to eat tonight...or do you want to heat up leftovers?" My yes is a logical reply since I do want to do one or the other. Plus it drives her crazy.
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JeffSaholDec 14 '11 at 18:41

Related: Does “either A or B ” preclude “both A and B”? - includes answers and comments discussing this issue, such as Which is why computer geeks and propositional calculus nerds will, when asked "do you want to go to lunch now or later?", answer "yes". (Illustrating that the "either" part is implied by context as often as it's cancelled by context.)
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aedia λDec 14 '11 at 19:09

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Often, a "yes" answer to an "or" question is a humorous way to express "both!" But a "yes, that's correct" answer to a "which is it, A or B?" question shows that the answerer utterly failed to comprehend the question.
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JPmiaouDec 14 '11 at 19:47

Perhaps next time you can change the question to use 'either, or' for an exclusive 'or' condition. I would like to see them answer that with a strait 'yes'
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JonDec 15 '11 at 7:59

'In practice, it's most unlikely that any conversation would proceed along those exact lines.' Unfortunately, you are wrong. I sent an email this morning that consisted of two, simple sentences, and my question was as simple as the example that I was given. The exact response was 'Yes. That is correct.' This wasn't the first time that I have heard this response to such a question, and this mornings incident simply made me curious.
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RLHDec 14 '11 at 18:36

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@RLH: I did say unlikely rather than impossible and I was thinking of a spoken conversation. All I can say is that it's a strange response and one which requires elucidation.
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Barrie EnglandDec 14 '11 at 18:41

Ah, sorry. My response was a bit stronger than I intended. You are correct that this is strange an not common. It's just fresh in my mind at the moment. I apologize if my tone was a tad offensive.
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RLHDec 14 '11 at 18:55

Actually, it is kind of a trendy joke response right now. It expresses enthusiasm. "Do you want ice cream or cake?" "Yes." It could also result from the listener not listening closely.
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RyanDec 14 '11 at 21:19

Well, "No" can in many cases also mean rejecting only a single choice but not the other.
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PacerierSep 24 '14 at 2:09

@Pacerier I am struggling to imagine a scenario where a person is asked "Do you want tea or coffee" (or any A or B) and they answer "No" meaning "No, I want coffee" (and expect to be understood)
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Mr. Shiny and New 安宇Sep 24 '14 at 14:05

It entirely depends on the context. And I was talking about written English, where punctuations exist in explicit forms. E.g. "Do you want (A or B)"? No.
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PacerierSep 24 '14 at 14:28

@Pacerier I still don't see how "No" can be interpreted as rejecting just one choice. In English, "or" is either exclusive or inclusive, but in either case, if one choice is wanted, then the answer has to be "yes".
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Mr. Shiny and New 安宇Sep 25 '14 at 1:31

The structure of the question is admittedly ambiguous. Some "A or B" questions do legitimately call for a yes or no answer. For example, I recently applied for insurance and the form had a question, "Have you ever been treated or diagnosed for diabetes, AIDS, or Hepatitis?" with boxes for "yes" or "no". In context, this was not an either/or question, like, "Which have you been treated for, diabetes or AIDS?", or "Were you treated for diabetes, or only diagnosed?" It was asking if any of the items on the list applied.

So the exact same question structure could call for different answers depending on the context:

"Do you have diabetes or hepatitis?" probably calls for a yes or a no.

"Do you want vanilla or chocolate?" probably calls for you to select one or the other.

In some cases a person might honestly misunderstand which is being asked. Like going back to the insurance form example, if the insurance company asks "Do you have type I or type II diabetes?", someone might honestly answer "yes", when the insurance company already knows he has one or the other and is trying to find out which one.

And by the way, giving a list of non-exhaustive choices in an "either/or" question and demanding the other person pick one is a classic propaganda technique. I read a gag survey once with the question: "In the past (and probably still in the present) there was a sinister conspiracy between the Scotts and the French to destroy England. Do you believe that, (a) The Scotts are more deceitful and underhanded than the French? (b) The French are more deceitful and underhanded than the Scotts? Or (c) There is nothing to choose between the two?" There are plenty of real "public opinion polls" that are only slightly less blatant.